1. Field of the Invention
This invention relates to fireplaces, and particularly to the metallic liner within a fireplace structure, commonly known as the firebox.
2. Description of the Prior Art
It is believed the art relating to this invention may be found in Class 126, sub-classes 120, 121, 130, 131 and 141. A search through this field of search has revealed the following U.S. Pat. Nos.: 1,306,612, 1,714,955, 2,494,527, 2,642,859, 2,703,567, 3,180,332, 3,995,611, 4,056,091, 4,013,059.
As indicated by the patents listed above, it appears that metal fireplace liners or fireboxes have been manufactured for many years. Initially, fireplaces were and still are in some instances fabricated from natural stone. In years past, the fireplace served primarily a utilitarian function in that it was used as a source of heat for cooking meals and for heating the residence. With the advent of the wood burning cook stove, the fireplace was not relied upon as extensively for the purpose of cooking, but it continued to be of importance with regard to heating the home. As technology advanced, however, other devices that worked more efficiently for heating the home were developed and the fireplace lost its primarily utilitarian function and became more of an aesthetic feature in the home.
Within the last decade, and perhaps even beyond, there has been a tendency to resurrect the utilitarian features of a fireplace so that it can again be used efficiently as a source of heat for heating the home. In most instances, it is not relied upon as the only source of heat, but it does provide an important adjunct to other more sophisticated and more costly sources of heat. To effectuate this end, fireboxes have been prefabricated which may be utilized as the fireplace liner within fireplace structures that are fabricated in many different styles and from many different materials. The most prevalent practice is to utilize fireproof or non-combustible materials as the fireplace structure to surround the firebox in such a manner as to thermally insulate the firebox from other combustible materials such as wood framing adjacent to the fireplace structure.
In many such fireplaces constructed from masonry products, such as cinder block, cement block, common red brick and other types of masonry products, a concrete pad is poured to support the fireplace structure. On the fireplace pad there is appropriately positioned the metallic firebox which in some instances is lined interiorly with fire brick. Around the outside of the firebox, and around at least a portion of the flu connected to the firebox for drawing products of combustion from the firebox, the masonry fireplace structure itself is usually constructed by skilled stone masons. The usual practice is to abut the masonry material contiguously against the outside surface of the metal firebox, so as to lend mechanical support to the firebox and to thermally insulate it from surrounding combustible materials.
One of the disadvantages of this practice is that the thermal coefficient of expansion and contraction of the heavy metallic firebox differ substantially from the thermal coefficient of expansion and contraction of the masonry products that surround it. The result is that when the metal is heated and expands against the non-elastic masonry, cracks are formed in the surrounding masonry structure that not only weaken the fireplace structure, but permit moisture to enter such cracks, especially if the crack is exposed on an exterior wall, and in any event, renders an otherwise attractive fireplace structure unsightly. Accordingly, it is one of the principal objects of the present invention to provide a fireplace structure, including a firebox, in which means are provided accommodating thermal expansion and contraction of the metallic firebox without imposing destructive forces on the surrounding masonry structure.
Prefabricated fireboxes for fireplaces are sometimes constructed with an inner liner and an outer liner spaced apart to provide an air space through which air may be channelled to increase the efficiency of the fireplace in heating the home. Most such conventional prefabricated fireboxes are constructed in such a manner that the inner liner is rigidly attached to the outer liner by gusset plates that are spot welded to both the inner and outer liner, thus precluding accommodation of differences in thermal expansion and contraction between the two liners and the surrounding masonry wall. Such a construction possess the same disadvantage as the construction discussed above in which the fireplace liner is surrounded directly by masonry, in that the outer liner is heated, expands and imposes a thermally induced tensile stress on the surrounding masonry. Accordingly, it is another object of the present invention to provide a prefabricated firebox for a fireplace structure in which the firebox is constructed to possess an inner liner and an outer liner and means are provided disposed between the two liners to accommodate different rates of expansion and contraction therebetween.
The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described, since it may be embodied in various forms within the scope of the appended claims.